Living polymerization (i.e., polymerization proceeding in the practical absence of chain transfer to monomer and irreversible termination) is a very useful method for designing polymer structures, permitting for example, versatile synthetic routes for the preparation of a wide variety of well-defined polymer structures, such as end-functionalized polymers, star-shaped polymers and/or block copolymers and control of the molecular weight and molecular weight distribution of the polymer, as well as enabling functional groups to be positioned at desired points in the polymer chain. Since Szwarc et al. demonstrated the living nature of polystyryllithium formed from the reaction of sodium naphthalene and styrene in the 1950s, a wide variety of living polymerization schemes have been developed, including cationic, anionic, radical, ring-opening, and group transfer polymerization. One of the most useful features of living polymerizations is the ability to prepare block copolymers. Living cationic sequential block copolymerization is generally recognized as one of the simplest and most convenient methods to provide well-defined block copolymers with high structural integrity.
Linear-, star-, and arborescent-block copolymers with a rubbery polyisobutylene (PIB) center block and glassy end blocks are useful thermoplastic elastomers, exhibiting excellent properties such as thermal and oxidative stability and biocompatibility. To date a large number of these block copolymers with polystyrene, poly(p-methylstyrene), poly(p-tert-butylstyrene), poly(p-chlorostyrene), poly(p-fluorostyrene), poly(α-methylstyrene) and polyindene as end blocks have been prepared.
All of the above thermoplastic elastomers contain a hydrophobic end blocks. Some applications, however, require block copolymers where the end blocks are hydrophilic. The ability to tune the overall hydrophilicity of the block copolymer would provide a wide range of useful products.